Amalgamation process



United States Patent 3,450,607 AMALGAMATION PROCESS Ronald L. Dotson, Baton Rouge, and Benjamin S. Lowry, Jr., Plaquemine, La., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Sept. 24, 1965, Ser. No. 490,124 Int. Cl. C23b 5/30, 1/00; C22d 1/26 US. Cl. 204-34 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for the amalgamation of ferrous surfaces and more particularly relates to a process for effectively producing a continuously amalgamated surface on a ferrous bed plate for use in an electrolytic cell for the production of chlorine from brine using a flowing mercury cathode.

For. many years, the problem of forming a continuous amalgam on the bed plate of mercury cells has been recognized, particularly where it is desired to form such amalgam in the presence of air. It is known that while iron will form an amalgam with mercury, the exposure of a clean ferrous surface to air or other oxygen-containing gas produces almost instantly a thin oxide coating on such surface rendering it substantially inert to mercury. Many problems have therefore been associated with the amalgamation of a mercury cell bed plate to prevent bare spots or non-amalgamated portions. If portions of such bed plate are not amalgamated before use, or if portions become unamalgamated during use, electrical efiiciency of the chlorine cell is reduced, excess iron contaminates the brine, large amounts of mercury butter are formed and excessive amounts of hydrogen are produced which contaminate the chlorine and create an explosion hazard.

It is an object of this invention to provide a process for the amalgamation of ferrous surfaces. It is an additional object of this invention to provide a process whereby ferrous mercury cell bed plates may be amalgamated in the presence of air to obtain a uniform, continuous amalgam on the surface thereof. These and other objects and advantages of the process will be readily understood by reference to the following detailed specification.

It has been discovered that a ferrous surface may be uniformly and continuously amalgamated by placing an inert conductive surface in close proximity to such ferrous surface, interposing a source of mercury between such surfaces and applying a low potential at high amperage between such surfaces where the ferrous surface is used as the cathode. Application of such potential causes uniform and continuous amalgamation of the mercury from the mercury source with the ferrous surface. Such a process may be used on small areas or large surfaces as desired, and produces a long-lasting amalgam on such surface.

The process of this invention may be used to amalgamate or reamalgamate spots or patches on bed plates which have been in use and show symptoms of having 3,450,607 Patented June 17, 1969 ice lost amalgamation on some portions without removing such bed plates from the cell. Likewise, this process may be employed to prepare a new bed plate for use. In preparing such ferrous surface for amalgamation, it is usually desirable to first brush with a wire brush, grind, or otherwise clean the surface to remove gross amounts of iron oxides or scale which passivate the surface to amalgamation. As fast as the gross oxide film is removed, however, a very thin oxide film will form which is not visible to the unaided eye but which again substantially passivates such surface. The expression cleaned ferrous metal surface as used herein means, therefore, a ferrous metal surface cleaned and contacted with air or other oxygen containing gas so that no oxide film is visible but such expression recognizes the presence of the very thin film of iron oxide which is not visible.

In conjunction with the ferrous metal surface, an additional conductive surface for use as an anode is necessary. Such additional conductive surface is preferably chemically inert to other materials employed in the process and is suitably made of graphite, titanium or the noble metals. Such inert conductive surface may be of any desired shape or size, depending usually upon the shape and size of the ferrous surface to be treated.

Between the cleaned ferrous metal surface and the inert conductive surface, a source of mercury is supplied. The mercury source is conveniently liquid metallic mercury as a layer on the ferrous surface but it may likewise be a soluble mercury salt in a carrier such as brine in the form of a liquid layer on the ferrous surface, or in any suitable form so long as it is in direct contact with the ferrous metal surface and electrical contact with the inert conductive surface.

The inert conductive surface is spaced in close proximity to the ferrous surface to be treated. It is usually desirable for the spacing to be sufiiciently close to allow arcing between the surfaces when the desired potential is applied. This is particularly desirable where a liquid mercury layer is employed as the mercury source. If such mercury layer is covered with an electrolyte such as brine, it is effective to use an inert gas pocket or sheath between the anode and cathode so that arcing may occur therebetween. When a soluble mercury salt is employed in a liquid carrier such as brine, arcing is not essential but it is desirable to space the anode and cathode in close proximity. A space of from 0.25 to 1 inch is generally suitable.

In order to achieve suitable amalgamation of the cleaned ferrous metal surface, it is necessary to provide an electrical potential of between from 3 to 15 volts, preferably from 6 to 12 volts. Less than 3 volts produces an inferior amalgam and amalgamation is very slow. If greater than 15 volts are employed a serious mercury vapor hazard is produced. A current of at least 0.5 amp is employed, preferably from about 10 to amps.

In the process of this invention as applied to a section of a mercury cell bed plate indicating incomplete amalga-mation or loss of amalgamation during operation, the cell is electrically isolated, opened and drained, and the bed plate section is cleaned with wire brushes or other abrading devices and washed with water to remove the dust. Mercury flow to the cell is then resumed by the cells mercury pump and one or more graphite electrodes are electrically connected as anodes to provide an amperage sufiicient to produce arcing, e.g., usually at least 10 amps and 6 to 15 volts difference in potential between the bed plate and the graphite anode. Suitable amalgamation is achieved in 1 to 3 minutes and the cell may be returned to normal operation.

In order to provide ease in understanding, the following examples are set forth to illustrate the invention but are not to be construed to limit the scope thereof.

3 EXAMPLE 1 A badly corroded area on a small mild steel plate was prepared for amalgamation by first abrading the corroded area to remove the heavy oxide coating and expose bare metal. A layer of metallic mercury was provided on the surface of the plate covering the area to be amalgamated, and a graphite anode /2 inch in diameter was spaced A inch above the surface of the steel plate. Between the steel plate covered with mercury and the carbon anode was passed a direct current of 60 amps at difference in potential of volts for a period of 1 minute. Arcing between the anode and cathode occurred continuously during this period. At the end of the treating period, the steel plate was washed to remove any excess mercury. The area thus treated was found to be uniformly and continuously amalgamated.

EXAMPLE 2 A small steel plate having a badly corroded area on the surface thereof was cleaned by abrading the surface to expose bare metal. The surface of the cleaned steel plate was then covered with a layer of mercury and a layer of saturated sodium chloride brine. A carbon anode /2 inch in diameter was employed which was surrounded 'by a glass tube sealed at the top. Nitrogen gas under positive pressure was continuously fed to the annular space between the carbon anode and a glass tube. The carbon anode was placed about A; inch above the steel plate and a potential of 12 volts at 60 amps applied between the anode andcathode for a period of 1 minute. Arcing occurred continuously during this period. At the end of the treatment period, the steel plate was washed with water .to remove any excess mercury and found to have a continuous and uniformly amalgamated surface in the area of treatment.

Various modifications can be made in the present invention without departing from the spirit or scope thereof for it is understood that we limit ourselves only as defined in the appended claims.

We claim:

1. A process for the amalgamation of ferrous surfaces which comprises:

(1) providing a cleaned ferrous metal surface,

' (2) providing an inert conductive surface as an anode in sufficiently close proximity to said cleaned ferrous metal surface to allow arcing between said anode and said ferrous metal surface,

{3) supplying a source of liquid metallic mercury between the ferrous surface and the inert conductive surface and in contact with the ferrous surface, and

(4) applying a difference in potential of from 3 to 15 volts at an amperage of at least 0.5 amp between said inert conductive surface and said ferrous surface to produce amalgamation of said ferrous surface.

2. The process of claim 1 wherein the difference in potential applied between the inert conductive surface and the ferrous surface is from 3 to 15 volts and the amperage is from about 10 to amps.

3. The process of claim 1 wherein the anode is composed of graphite.

4. The process of claim 3 wherein the difference in potential between the inert conductive surface and the ferrous surface is from 6 to 12 volts and the amperage is from about 10 to 150 amps.

References Cited UNITED STATES PATENTS 318,932 5/1885 Trippe 209-179 1,863,254 6/1932 Polin 204l24 2,547,536 4/1951 Pollard 11751 2,567,762 9/1951 Burkholder l1751 HOWARD S. WILLIAMS, Primary Examiner.

D. R. JORDAN, Assistant Examiner.

US. Cl. X.R. 

